The invention concerns a chain stitch sewing mechanism with a sewing head movable parallel to a sewn material plane, including a needle rod for a thread carrying needle, a needle drive for a moving the needle rod linearly back and forth at an angle to the sewn material plane, a needle shaped thread catcher provided with an open catching hook and a catcher drive for linearly moving the thread catcher back and forth at an angle to the sewn material plane, with the movement paths of the needle and of the thread catcher forming a sharp angle with one another whose apex lies below the sewn material plane, and with the needle drive and the catcher drive being so controlled that upon a withdrawal of the needle from the sewn material a thread loop is formed below the sewn material which is caught by the thread catcher and pulled upwardly through the sewn material.
Such a sewing mechanism is, for example, known from DE 197 51 011 A1. In the solution described there, the thread catcher during its up and down movement is also driven oscillatingly in rotation about its linear movement direction. Upon the insertion of the thread catcher into the sewn material, the thread catcher takes on a rotary position at which the hook opening is oriented at least nearly in the advancement direction of the sewing head, so that the thread loop upon the moving forwardly of the sewing head does not slip from the catcher and the new loop can be drawn through the preceding loop to make possible a true chaining of the loops. However, before the upward movement of the thread catcher with the newly caught loop the thread catcher is pivoted to a rotary position at which the hook opening faces nearly oppositely to the transport direction of the sewing head to avoid the loop lying on the upper surface of the sewn material being caught again by the hook during the upward movement of the thread catcher. In order to move the thread catcher both linearly up and down and also to rotate it back and forth about its linear movement path, a complicated mechanism necessary.